Many systems require a wiring and/or electrical contacts in order to supply electrical power to devices. Omitting these wires and contacts provides for an improved user experience. Traditionally, this has been achieved using batteries located in the devices but this approach has a number of disadvantages including extra weight, bulk and the need to frequently replace or recharge the batteries. Recently, the approach of using wireless inductive power transfer has received increasing interest.
Part of this increased interest is due to the number and variety of portable and mobile devices having exploded in the last decade. For example, the use of mobile phones, tablets, media players etc. has become ubiquitous. Such devices are generally powered by internal batteries and the typical use scenario often requires recharging of batteries or direct wired powering of the device from an external power supply.
As mentioned, most present day devices require a wiring and/or explicit electrical contacts to be powered from an external power supply. However, this tends to be impractical and requires the user to physically insert connectors or otherwise establish a physical electrical contact. It also tends to be inconvenient to the user by introducing lengths of wire. Typically, power requirements also differ significantly, and currently most devices are provided with their own dedicated power supply resulting in a typical user having a large number of different power supplies with each power supply being dedicated to a specific device. Although, internal batteries may prevent the need for a wired connection to an external power supply, this approach only provides a partial solution as the batteries will need recharging (or replacing which is expensive). The use of batteries may also add substantially to the weight and potentially cost and size of the devices.
In order to provide a significantly improved user experience, it has been proposed to use a wireless power supply wherein power is inductively transferred from a transmitter coil in a power transmitter device to a receiver coil in the individual devices.
Power transmission via magnetic induction is a well-known concept, mostly applied in transformers which have a tight coupling between the primary transmitter coil and the secondary receiver coil. By separating the primary transmitter coil and the secondary receiver coil between two devices, wireless power transfer between the devices becomes possible based on the principle of a loosely coupled transformer.
Such an arrangement allows a wireless power transfer to the device without requiring any wires or physical electrical connections. Indeed, it may simply allow a device to be placed adjacent to, or on top of, the transmitter coil in order to be recharged or powered externally. For example, power transmitter devices may be arranged with a horizontal surface on which a device can simply be placed in order to be powered.
Furthermore, such wireless power transfer arrangements may advantageously be designed such that the power transmitter device can be used with a range of power receiver devices. In particular, a wireless power transfer standard known as the Qi standard has been defined and is currently being developed further. This standard allows power transmitter devices that meet the Qi standard to be used with power receiver devices that also meet the Qi standard without these having to be from the same manufacturer or having to be dedicated to each other. The Qi standard further includes some functionality for allowing the operation to be adapted to the specific power receiver device (e.g. dependent on the specific power drain).
The Qi standard is developed by the Wireless Power Consortium and more information can e.g. be found on their website: http://www.wirelesspowerconsortium.com/index.html, where in particular the defined Standards documents can be found.
Wireless power transfer systems are applied in an increasing variety and number of applications. For example, work is ongoing to expand the Qi power transfer standard to include high power applications with the potential of powers of up to more than 1 kW. Such high power capability leads to wireless power transfer systems being practical for more and more applications. However, this also introduces more challenges and specifically increases the risk of undesirable situations occurring. Thus, there is a desire to introduce control aspects to wireless power transfer systems which mitigate the risk of undesirable or even potentially unsafe scenarios occurring.
For example, it is envisaged that wireless power transfer may be used in a kitchen environment to power to various kitchen appliances and devices, including high power devices such as kettles, pans, blenders etc.
However, in such embodiments, additional considerations must be taken into account to ensure that undesired and unsafe scenarios do not occur. This must also consider the potential behavior of the user. For example, in the kitchen application there may be a range of power provision points including some intended for heating pans or kettles, some intended for other devices such as blenders, mixers etc. The specific layout and materials used may depend on a number of issues, including aesthetic and design preferences, and therefore different parts may use different materials etc.
However, users will generally not consider such aspects and will typically not be focused on where devices can be positioned. For example, the user may not consider that some devices should be restricted to specific areas or parts of the worktop due to their power transfer characteristics or application.
Hence, an improved power transfer system would be advantageous and in particular a system allowing an improved user experience, increased reliability, increased flexibility, facilitated implementation, improved safety and/or improved performance would be advantageous.